Remove all staples and upholstery tacks using needle nose pliers. Carefully lift away all fabric and batting. You will use the old fabric pieces to create a pattern for the new upholstery fabric you are using.
Lay each old piece out on top of your new upholstery fabric. Cut around each template, leaving a 2-inch to 3-inch overhang.
Staple batting over all bare areas on the chair, paying particular attention to the seat and arms for comfort. Be sure to pull the batting taut over each area as you staple it into place. You may also opt to secure the batting with upholstery tacks, using a rubber mallet to hammer them into place.
Place the fabric over the back of the chair, pulling through the sides and around to the back. Pull snugly and staple, working on first the top, then bottom before stapling each side. Lay the seat fabric into place and pull through to the underside of the chair. Staple securely into place.
Drape the fabric over the chair arms. Fold the back third of the fabric forward, toward you. Staple the fabric snugly on each side, leaving the front and back edges loose at this point. Cut a slit in the center of the folded portion of fabric to allow it to wrap back around the armchair. Wrap the fabric, forming pleats and gathers at the back of the chair arms. Pull the fabric at the front of the chair arm downward and secure. Then pleat or gather the excess fabric at each side toward the center neatly and staple or tack into place.
Cover the chair back with fabric. Fold the edges under and secure with upholstery tacks or staples. If you use staples, use an upholstery trim to cover exposed staples. Many upholstery tacks are quite attractive and suitable for use in a visible area. Use welting, piping or other accents as desired, applying with a glue gun or upholstery tacks. Enjoy your armchair reupholstery job.